Transmitter, receiver, transmission method, and reception method

ABSTRACT

In a transmitter, an assignment circuit maps a phase tracking reference signal (PT-RS) onto a subcarrier, and a transmitting circuit transmits a signal containing the phase tracking reference signal. The phase tracking reference signal is mapped onto a different subcarrier for each cell, group, or mobile station.

TECHNICAL FIELD

The present disclosure relates to a transmitter, a receiver, atransmission method, and a reception method.

BACKGROUND ART

A communication system called “fifth-generation mobile communicationsystem (5G)” has been under consideration. In 5G, flexible provision ofa function to each of various use cases where an increase incommunication traffic, an increase in the number of terminals to beconnected, high reliability, low latency, and the like are needed hasbeen under consideration. There are three typical use cases: enhancedMobile Broadband (eMBB), Massive Machin Type Communications (mMTC), andUltra Reliable and Low Latency Communications (URLLC). In 3GPP (3rdGeneration Partnership Project), which is an internationalstandardization organization, sophistication of communication systemshas been under consideration from the embodiment of both sophisticationof LTE systems and New RAT (Radio Access Technology) (see, for example,NPL 1).

CITATION LIST Non Patent Literature

NPL 1: RP-161596, “Revision of SI: Study on New Radio AccessTechnology”, NTT DOCOMO, September 2016

NPL 2: R1-1612335, “On phase noise effects”, Ericsson, November 2016

SUMMARY OF INVENTION

In New RAT, as compared with LTE/LTE-Advanced, signals of highfrequencies of, for example, 6 GHz or higher are utilized as carrierwaves. In particular, in a case where a high frequency band and ahigher-order modulation multivalued number (modulation order) are used,error rate characteristics deteriorate due to a CPE (common-phase error)or ICI (inter-carrier interference) that occurs due to the phase noiseof a local oscillator of a transmitter (see, for example, NPL 2). Toaddress this problem, New RAT has given consideration to a receiver'sperforming a CPE correction or ICI correction (hereinafter sometimesreferred to as “CPE/ICI correction”) by means of a phase trackingreference signal (PT-RS) in addition to performing channel equalization.

However, no close consideration has been given to a method forsuppressing interference with PT-RSs that are transmitted from aplurality of base stations (BSs; sometimes referred to as “gNBs”) or aplurality of mobile stations (terminals; sometimes referred to as “UEs(pieces of user equipment)”).

An embodiment of the present disclosure facilitates providing atransmitter, a receiver, a transmission method, and a reception methodthat can appropriately suppress interference with PT-RSs that aretransmitted from a plurality of base stations or mobile stations.

According to an embodiment of the present disclosure, there is provideda transmitter including an assignment circuit that maps a phase trackingreference signal onto a subcarrier and a transmitting circuit thattransmits a signal containing the phase tracking reference signal. Thephase tracking reference signal is mapped onto a different subcarrierfor each cell, group, or mobile station.

According to an embodiment of the present disclosure, there is provideda receiver including a receiving circuit that receives a signalcontaining a phase tracking reference signal and a demodulating circuitthat demodulates a data signal by using a phase noise estimated valuecalculated using the phase tracking reference signal. The phase trackingreference signal is mapped onto a different subcarrier for each cell,group, or mobile station.

According to an embodiment of the present disclosure, there is provideda transmission method including mapping a phase tracking referencesignal onto a subcarrier and transmitting a signal containing the phasetracking reference signal. The phase tracking reference signal is mappedonto a different subcarrier for each cell, group, or mobile station.

According to an embodiment of the present disclosure, there is provideda reception method including receiving a signal containing a phasetracking reference signal and demodulating a data signal by using aphase noise estimated value calculated using the phase trackingreference signal. The phase tracking reference signal is mapped onto adifferent subcarrier for each cell, group, or mobile station.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination of a method, anapparatus, an integrated circuit, a computer program, and a storagemedium.

An embodiment of the present disclosure makes it possible toappropriately suppress interference with PT-RSs that are transmittedfrom a plurality of base stations or mobile stations.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an example of mapping of DMRSs and PT-RSs.

FIG. 2 shows a configuration of a part of a transmitter according toEmbodiment 1.

FIG. 3 shows a configuration of a part of a receiver according toEmbodiment 1.

FIG. 4 shows a configuration of the transmitter according to Embodiment1.

FIG. 5 shows a configuration of the receiver according to Embodiment 1.

FIG. 6 shows a process of the transmitter according to Embodiment 1.

FIG. 7 shows a configuration of the receiver according to Embodiment 1.

FIG. 8 shows an example of mapping of PT-RSs according to an operationexample of Embodiment 1.

FIG. 9 shows an example of mapping of PT-RSs according to OperationExample 1 of Embodiment 2.

FIG. 10 shows an example of mapping of PT-RSs according to OperationExample 2 of Embodiment 2.

FIG. 11 shows an example of mapping of PT-RSs according to OperationExample 1 of Embodiment 3.

FIG. 12 shows an example of mapping of PT-RSs according to OperationExample 2 of Embodiment 3.

FIG. 13 shows an example of mapping of PT-RSs according to OperationExample 3 of Embodiment 3.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure are described in detail below withreference to the drawings.

When a signal is assigned to a higher frequency band or when a highermodulation multivalued number is used for a signal, CPE/ICI exerts agreater influence on error rate characteristics. Accordingly, asmentioned above, in a case where a high frequency band and ahigher-order modulation multivalued number are used, a receiver'sperforming a CPE/ICI correction by means of a PT-RS in addition toperforming channel equalization has been under consideration.

For tracking of CPE/ICI, which randomly fluctuates over time, PT-RSs aremore densely mapped onto a time axis than channel estimating(demodulating) reference signals (DMRSs: demodulation referencesignals). Specifically, it is assumed that the density of allocation ofPT-RSs that are mapped in a time domain is set, as in the case of theallocation of PT-RSs onto every symbol, every symbol out of two adjacentsymbols, every symbol out of four adjacent symbols, or the like.Further, since CPE/ICI has the characteristics of fluctuating littlebetween subcarriers, PT-RSs are comparatively less densely mapped in afrequency domain. Specifically, it is assumed that the density ofallocation of PT-RS that are mapped in the frequency domain is set, asin the case of the allocation of PT-RSs onto one subcarrier per RB(resource block), one subcarrier per two adjacent RBs, one subcarrierper four adjacent RBs, or the like.

According to the agreements about PT-RSs in 3GPP RAN1#88, PT-RSs areused between a base station (BS, eNB, gNB) and a mobile station(terminal, UE) notified from the base station by higher layer signaling(e.g. RRC (radio resource control) signaling). Further, it is assumedthat the density of allocation of PT-RSs in the time domain and thefrequency domain flexibly varies according to a modulation multivaluednumber, a bandwidth, or the like that is used between the base stationand the mobile station.

Further, a method by which a mobile station determines the density ofallocation of PT-RSs has been under consideration. One method is amethod by which the density of allocation of PT-RSs is notified by aPT-RS dedicated control signal from a base station (explicitnotification). Another method is a method by which a correspondencerelationship between the density of allocation of PT-RSs and a differentparameter (e.g. a modulation multivalued number or a bandwidth) isdetermined in advance and the mobile station determines the density ofallocation of PT-RSs with reference to the different parameter and itscorrespondence relationship, which are notified with DCI (downlinkcontrol information) during communication (implicit notification). Itshould be noted that there is a possibility that a method other thanthese methods might be used.

Meanwhile, DMRSs for use in channel estimation, whose channelcharacteristics greatly vary in a frequency domain and do not as greatlyvary in a time domain as phase noise, are more densely mapped onto thefrequency domain and less densely mapped onto the time domain thanPT-RSs. Furthermore, in New RAT, for earlier timing of datademodulation, the introduction of front-loaded DMRSs, which areallocated at the front of slots, is assumed.

Further, in New RAT, it is assumed that MIMO (multiple-input andmultiple-output) is used. That is, a base station and one or more mobilestations located within a cell constituted by the base station arecapable of transmission and reception through a plurality of antennaports corresponding to different beams (precodings) that use the sametime and frequency resources. Since the base station and the mobilestation are each limited in maximum transmission power, it is assumedthat they are operated so that a total of transmission power of aplurality of antenna ports that are used for data transmission does notexceed the maximum value of transmission power. Accordingly,transmission power per antenna port can be made greater in a case wheretransmission is done with one antenna port than in a case wheretransmission is done with a plurality of antenna ports.

The application of the same precoding to PT-RSs as antenna ports throughwhich to transmit DMRSs (also sometimes referred to as “DMRS ports”) hasbeen under consideration, and it is also conceivable that PT-RSs may bedefined as part of DMRSs. In this case, DMRSs that are used as PT-RSsare more densely mapped in the time domain and less densely mapped inthe frequency domain than other DMRSs. Further, reference signals thatare used for correction of CPE/ICI that occurs due to phase noise may becalled in a name different from “PT-RS”.

Further, PT-RSs are transmitted and received between a base station andeach mobile station located within a cell constituted by the basestation. Note here that since a group of antenna ports that share alocal oscillator of a transmitter (in a downlink, a base station; in anuplink, a mobile station) are equal in value of CPE/ICI, PT-RSs needonly be transmitted from any antenna port within the group and do notneed to be transmitted from all of the antenna ports within the group.Therefore, the number of antenna ports through which to transmit andreceive data may be smaller than the number of antenna ports throughwhich to transmit and receive PT-RSs.

Furthermore, it is conceivable that a PT-RS that is transmitted to onemobile station may be orthogonally multiplexed onto data. Further, it isalso conceivable that PT-RSs may be subjected to FDM (frequency divisionmultiplexing) onto each other. Therefore, in a case where when a PT-RSof one antenna port is transmitted over one RE (resource element), dataor a PT-RS of another antenna port is not transmitted over the same RE.

For this reason, it is conceivable that the transmission power of oneantenna port of a PT-RS per RE may be greater than the transmissionpower of one antenna port of data per RE. As mentioned above, PT-RSsinterfere with each other, as they are transmitted from a base station(downlink) that constitutes a plurality of cells or from a plurality ofmobile stations (uplink). In so doing, the magnitude of interferencethat a PT-RS that is transmitted from an antenna port causes withanother cell is greater than the magnitude of interference that datathat is transmitted from an antenna port causes with another cell.

FIG. 1 shows an example of mapping of DMRSs and PT-RSs in MIMO. Thenumbers in the REs on which DMRSs and PT-RSs are mapped represent portnumbers. That is, DMRSs and PT-RSs of the same number in FIG. 1 share aprecoding.

Further, in NR (New Radio), the use of a CF-OFDM (cyclicprefix—orthogonal frequency division multiplexing) scheme is assumed ina downlink (direction from a base station to a mobile station).Meanwhile, in an uplink (direction from a mobile station to a basestation), both the CP-OFDM scheme and a DFT-S-OFDM (discrete Fouriertransform—spread OFDM) scheme are under consideration, and for example,switching between communication schemes according to communicationenvironment for use is assumed.

For example, in the case of a downlink, when a PT-RS that is transmittedfrom a base station to which a mobile station is connected is present inthe same RE as a PT-RS that is transmitted from another base station,the PT-RSs collide with each other. At this time, in a case where thetransmission power of a PT-RS per RE of one antenna port is higher thanthe transmission power of data, the amount of inference between thePT-RSs is larger than in a case where the data and the PT-RS and thedata collide with each other. Similarly, in the case of an uplink, acollision between a PT-RS that is transmitted from a mobile station towhich a base station is connected and a PT-RS that is transmitted fromanother mobile station connected to another base station makes theamount of inference between the PT-RSs larger than in a case where dataand a PT-RS collide with each other.

Embodiments of the present disclosure describe methods for suppressing acollision between PT-RSs and preventing an increase in amount ofinterference.

Embodiment 1 Brief Overview of Communication System

A communication system according to the present embodiment includes atransmitter 100 and a receiver 200. That is, in a downlink, thetransmitter serves as a base station, and the receiver serves as amobile station. Further, in an uplink, the transmitter serves as amobile station, and the receiver serves as a base station.

FIG. 2 is a block diagram showing a configuration of a part of thetransmitter 100 according to the present embodiment. As shown in FIG. 2,the transmitter 100 includes a signal assigner 106 (assignment circuit)that maps a phase tracking reference signal (PT-RS) onto a subcarrierand a transmitting unit 107 (transmitting circuit) that transmits asignal containing the PT-RS.

FIG. 3 is a block diagram showing a configuration of a part of thereceiver 200 according to the present embodiment. As shown in FIG. 3,the receiver 200 includes a receiving unit 202 (receiving circuit) thatreceives a signal containing a PT-RS and a data demodulator 207 thatdemodulates a data signal by using a phase noise estimated value(CPE/ICI estimated value) calculated using the phase-tracking referencesignal (PT-RS).

Note here that the PT-RS is mapped onto a different subcarrier for eachcell, group, or mobile station.

Configuration of Transmitter

FIG. 4 is a block diagram showing a configuration of the transmitter 100according to the present embodiment. As shown in FIG. 4, the transmitter100 includes a PT-RS generator 101, a hopping pattern generator 102, afrequency hopper 103, an error correction coder 104, a modulator 105,the signal assigner 106, the transmitting unit 107, and an antenna 108.

The PT-RS generator 101 generates a PT-RS and outputs the PT-RS thusgenerated to the frequency hopper 103.

The hopping pattern generator 102 determines a hopping pattern (e.g. theinitial position of the PT-RS and a hopping offset) by using at leastone of a cell ID, a group ID, a UE ID (mobile station ID), a slotnumber, and the like. The hopping pattern may be calculated, forexample, from a specified hopping pattern generating formula. Thehopping pattern generator 102 outputs the hopping pattern thusdetermined to the frequency hopper 103.

For example, the cell ID is a cell ID that corresponds to a base stationto which a mobile station is connected, the group ID is an ID of a groupto which a mobile station belongs, and the UE ID is an ID of a mobilestation.

The frequency hopper 103 causes the PT-RS inputted from the PT-RSgenerator 101 to hop from one position to another every unit time (suchas symbol, slot, mini slot, sub-frame, or frame) in accordance with thehopping pattern inputted from the hopping pattern generator 102 andoutputs, to the signal assigner 106, the PT-RS subjected to hopping. Itshould be noted that the frequency hopper 103 may output the PT-RS tothe signal assigner 106 without performing frequency hopping on thePT-RS.

The error correction coder 104 receives a transmit data signal, subjectsthe transmit data signal to error correction coding, and outputs thesignal subjected to the error correction coding to the modulator 105.

The modulator 105 performs a modulation process on the signal inputtedfrom the error correction coder 104 and outputs the data signal thusmodulated to the signal assigner 106.

The signal assigner 106 maps a DMRS, the data signal inputted from themodulator 105, and the PT-RS inputted from the frequency hopper 103 ontotime and frequency domains and outputs the signals thus mapped to thetransmitting unit 107.

The transmitting unit 107 subjects the signals inputted from the signalassigner 106 to a radio transmission process such as frequencyconversion through carrier waves and outputs the signals subjected tothe radio transmission process to the antenna 108.

The antenna 108 emits, toward the receiver 200, the signals inputtedfrom the transmitting unit 107.

Configuration of Receiver

FIG. 5 is a block diagram showing a configuration of the receiver 200according to the present embodiment. As shown in FIG. 5, the receiver200 includes an antenna 201, a receiving unit 202, a hopping patterngenerator 203, a signal demultiplexer 204, a channel estimator 205, aCPE/ICI estimator 206, a data demodulator 207, and an error correctiondecoder 208.

The antenna 201 receives a signal transmitted from the transmitter 100(see FIG. 4) and outputs the received signal to the receiving unit 202.

The receiving unit 202 subjects the received signal inputted from theantenna 201 to a radio reception process such as frequency conversionand outputs the signal subjected to the radio reception process to thesignal demultiplexer 204.

As is the case with the transmitter 100 (hopping pattern generator 102),the hopping pattern generator 203 determines, by using at least one of acell ID, a group ID, a UE ID, a slot number, and the like, the hoppingpattern (e.g. the initial position of a PT-RS and a hopping offset) usedfor the transmission of the PT-RS. The hopping pattern may be calculatedfrom the same hopping pattern generating formula as the hopping patterngenerating formula that the transmitter 100 uses. The hopping patterngenerator 203 outputs the hopping pattern thus determined to the signaldemultiplexer 204.

The signal demultiplexer 204 uses the hopping pattern inputted from thehopping pattern generator 203 to identify, from inside the signalinputted from the receiving unit 202, the positions in the time andfrequency domains on which the data, the DMRS, and the PT-RS are mappedand demultiplexes the signals from one another. Of the signals thusdemultiplexed, the signal demultiplexer 204 outputs the data to the datademodulator 207, outputs the DMRS to the channel estimator 205 and theCPE/ICI estimator 206, and outputs the PT-RS to the CPE/ICI estimator206.

The channel estimator 205 estimates channel information by using theDMRS inputted from the signal demultiplexer 204 and outputs the channelestimation information (channel information) to the data demodulator207.

The CPE/ICI estimator estimates CPE/ICI by using the PT-RS and DMRSinputted from the signal demultiplexer 204 and outputs a CPE/ICIestimated value to the data demodulator 207.

The data demodulator 207 demodulates, by using the channel estimationinformation inputted from the channel estimator 205 and the CPE/ICIestimated value inputted from the CPE/ICI estimator 206, the data signalinputted from the signal demultiplexer 204. The data demodulator 207outputs the demodulated signal to the error correction decoder 208.

The error correction decoder 208 decodes the demodulated signal inputtedfrom the demodulator 207 and outputs a received data signal thusobtained.

Operation of Transmitter 100 and Receiver 200

The following describes in detail how the transmitter 100 and thereceiver 200 operate.

FIG. 6 shows an example of the flow of a process of the transmitter 100,and FIG. 7 shows an example of the flow of a process of the receiver200.

In FIG. 6, the transmitter 100 determines a frequency resource(subcarrier) onto which to map a PT-RS (ST101). Further, the transmitter100 may also perform frequency hopping on the PT-RS.

Next, the transmitter 100 maps the PT-RS onto the frequency resourcedetermined in ST101 (ST102). Then, the transmitter 100 transmits asignal containing the PT-RS to the receiver 200 (ST103).

Meanwhile, as is the case with the transmitter 100 (ST101), the receiver200 determines a frequency source (subcarrier, hopping pattern) ontowhich the PT-RS is mapped (ST201). Next, on the basis of the frequencyresource determined in ST201, the receiver 200 demultiplexes the PT-RS(and a DMRS and data) from the signal transmitted from the transmitter100 (ST202). Next, the receiver 200 performs a CPE/ICI estimation byusing the PT-RS (and the DMRS) (ST203). Then, the receiver 200demodulates the data by using a CPE/ICI estimated value (ST204).

In so doing, the PT-RS transmitted from the transmitter 100 is mappedonto a different subcarrier for each cell, group, or mobile station.This makes it possible to prevent the PT-RS transmitted from thetransmitter 100 from being transmitted over the same subcarrier as aPT-RS of another cell, group, or mobile station, thus making it possibleto reduce collisions between PT-RSs. That is, this makes it possible toreduce the possibility that the PT-RS transmitted from the transmitter100 may suffer interference from a PT-RS of another cell, group, ormobile station.

It should be noted that subcarriers onto which PT-RSs are mapped may beassociated with each separate cell ID, group ID, or UE ID or may benotified from a base station to a mobile station by higher layersignaling.

The following describes methods (i.e. the processes in ST 101 shown inFIG. 6 and ST201 shown in FIG. 7) by which the transmitter 100 and thereceiver 200 determine frequency resources (subcarriers) onto which tomap PT-RSs.

It should be noted that the following describes a case where PT-RSs aresubjected to frequency hopping every slot.

Operation Example

According to this operation example, in the first slot in a frame ontowhich PT-RSs are mapped, the PT-RSs are mapped at regular spacings in auniformly-distributed manner in the frequency domain. Further, in asubsequent slot of the frame, identical hopping offsets are applied toall PT-RSs within an assigned band of a mobile station.

That is, in the operation example according to the present embodiment,the transmitter 100 performs frequency hopping on the PT-RSs so thatsubcarriers onto which the PT-RSs are mapped in each slot are uniformlydistributed at regular spacings. In other words, the transmitter 100(signal assigner 106) maps, at regular spacings in the frequency domain,a plurality of PT-RSs that are transmitted in each slot (at a giventime).

For example, the transmitter 100 (hopping pattern generator 102) and thereceiver 200 (hopping pattern generator 203) determine the initialpositions of PT-RSs and hopping offsets in the following way.

The following assumes that the size of the assigned band of the mobilestation is “N_(UE_BW) [RB]” and the density of allocation in thefrequency domain of PT-RSs that are mapped to the mobile station is “oneper N_(density) [RB]”.

First, a method is described by which to determine the frequencypositions of PT-RSs (i.e. the initial positions of PT-RSs) in the firstslot in a frame onto which the PT-RSs are allocated.

The transmitter 100 selects one subcarrier as an initial position fromamong N_(UE_BW) RBs (1 RB=12 subcarriers here) assigned to the mobilestation and maps a PT-RS onto the subcarrier in the initial positionthus selected. In selecting an initial position (subcarrier), thetransmitter 100 uses a pseudo-random number function and at least one of“the cell ID, the group ID, and the UE ID”. This allows as differentsubcarriers as possible to be selected among different cells, differentgroups, or different mobile stations.

Next, in an RB located N_(density) away from the RB on which theaforementioned PT-RS is allocated, the transmitter 100 maps a PT-RS ontothe same subcarrier as the subcarrier of the RB on which theaforementioned PT-RS is mapped. The transmitter 100 repeats this processuntil PT-RSs are mapped onto N_(UE_BW)/N_(density) subcarriers (i.e. onall RBs onto which PT-RSs are mapped).

Since each of the RBs within the assigned band onto which PT-RSs aremapped is identical in PT-RS initial position (subcarrier) to the otherone of the RBs, the PT-RSs in the first slot are uniformly mapped atregular spacings in the frequency domain.

Next, a method is described by which to determine hopping offsetsagainst PT-RSs in the second and subsequent slots.

The transmitter 100 selects one hopping set from among [0, 1, 2, . . . ,12N_(density)−1], and the value thus selected is “f_(HOP)”. It should benoted that in selecting a hopping offset, the transmitter 100 uses apseudo-random number function, at least one of “the cell ID, the groupID, and the UE ID”, and a slot number. This allows as different hoppingoffsets as possible to be selected among different cells, differentgroups, different mobile stations, or different slots.

In each slot, the transmitter 100 maps PT-RSs onto subcarriers locatedf_(HOP) away from all subcarriers on which N_(UE_BW)/N_(density) PT-RSsare mapped in a slot preceding the slot. The transmitter 100 repeatsthis process for each slot until the frame ends.

Further, through a process which is similar to that of theaforementioned transmitter 100, the receiver 200 identifies hoppingpatterns (initial positions and hopping offsets) and identifiessubcarrier positions onto which PT-RSs transmitted from the transmitter100 are mapped.

FIG. 8 shows an example of mapping of PT-RSs in the operation exampleaccording to the present embodiment.

In FIG. 8, the density of allocation of PT-RSs in the frequency domainis “one per RB” (in FIG. 8, one per twelve subcarriers). Therefore, inFIG. 8, in any slot, a PT-RS is mapped on one subcarrier in every RB ofthe assigned band of the mobile station. Further, frequency hopping ofthe PT-RSs is performed at the boundary between slots.

As shown in FIG. 8, the initial positions of the PT-RSs in Slot #0 arethe same subcarriers (fourth subcarriers of each separate RB) in eachseparate RB (FIG. 8 shows two RBs). Further, as shown in FIG. 8, thehopping offset f_(HOP) equals 7 subcarriers. Therefore, in Slot #1, thePT-RSs are mapped onto subcarriers (eleventh subcarriers of eachseparate RB) located f_(HOP)=7 subcarriers away from the subcarriersonto which the PT-RSs were mapped in each separate RB of Slot #0.

That is, as shown in FIG. 8, in each slot including the first andsubsequent slots, frequency spacings between PT-RSs are uniformly thesame (in FIG. 8, one RB (twelve subcarriers).

The foregoing has described the operation example according to thepresent embodiment.

Thus, in the present embodiment, a PT-RS is mapped onto a differentsubcarrier for each cell, group, or mobile station. For example, thetransmitter 100 determines, according to “the cell ID, the group ID, orthe UE ID” or higher layer signaling, a subcarrier onto which to map thePT-RS. This allows the PT-RS to be mapped onto a different subcarrierfor each cell, group, or mobile station.

In this way, a plurality of the transmitters 100 that correspond todifferent cells, different groups, or different mobile stations,respectively, become more likely to transmit PT-RSs by using differentfrequency resources (subcarriers) in the same time domain (e.g. in thesame slot).

This makes it possible, for example, in a downlink, to reduce collisionsbetween PT-RSs that are transmitted from the base station (transmitter100) to which the mobile station (receiver 200) is connected and PT-RSsthat are transmitted from another base station (another transmitter100). Similarly, this makes it possible, in an unlink, to reducecollisions between PT-RSs that are transmitted from the mobile station(transmitter 100) to which the base station (receiver 200) is connectedand PT-RSs that are transmitted from another mobile station (anothertransmitter 100) connected to another base station.

Therefore, the present embodiment makes it possible to appropriatelysuppress interference by reducing collisions between PT-RSs that aretransmitted from a plurality of base stations or mobile stations.

Further, the transmitter 100 applies frequency hopping to a PT-RS. In sodoing, a hopping pattern of the PT-RS is determined on the basis of “thecell ID, the group ID, or the UE ID” and a time-domain index (e.g. aslot number). This makes it more likely that different hopping patternsare used among different cells, groups, or mobile stations and thereforemakes it less likely that a PT-RS that the transmitter 100 transmitssuffer interference from a PT-RS of another cell, group, or mobilestation. That is, interference caused by collisions between PT-RSs amongdifferent cells, groups, or mobile stations is randomized. Further, byvarying hopping patterns according to the time-domain index in additionto “the cell ID, the group ID, or the UE ID”, a plurality of PT-RSs aremapped onto the same subcarrier in a certain slot according to “the cellID, the group ID, or the UE ID”, and even in the event of collisionsbetween PT-RSs, continued collisions between PT-RSs over a plurality ofslots can be prevented.

Further, in the first slot in a frame onto which PT-RSs are mapped, thetransmitter 100 maps the PT-RSs at regular spacings in auniformly-distributed manner in the frequency domain, and in asubsequent slot, the transmitter 100 applies identical hopping offsetsto all PT-RSs within the assigned band of the mobile station. As aresult, subcarriers onto which the PT-RSs are mapped are uniformlydistributed at regular spacings in each slot, so that the PT-RSs becomerobust against the frequency selectivity of channels.

Further, because of the setting in which “the density of allocation ofPT-RSs in the frequency domain is one per n (integer) RBs”, subcarrierpositions onto which PT-RSs are mapped within each separate RB includedin the assigned band of the mobile station are identical among the RBs.This eliminates the need for the receiver 200 to identify, for each RB,a subcarrier position onto which a PT-RS is mapped and therefore makesit possible to reduce the amount of calculation of the receiver 200.

Modification 1 of Embodiment 1

Although Embodiment 1 has illustrated a case where the number of PT-RSantenna ports is 1 (see, for example, FIG. 8), the number of PT-RSantenna ports may be 2 or larger. In a case where the number of PT-RSantenna ports is more than one, the transmitter 100 may for exampleselect the initial positions of PT-RSs so that the PT-RSs are mappedonto different subcarriers according to antenna port numbers in additionto “the cell ID, the group ID, or the UE ID”. Note, however, thathopping offsets against PT-RSs that are transmitted from the pluralityof antenna ports, respectively, take on identical values. This isintended to avoid the occurrence of a collision between PT-RS ports dueto frequency hopping.

Modification 2 of Embodiment 1

Further, in a case where there is coordination among cells and the cellsshare information as to how PT-RSs are mapped in each cell, these cellsmay be subjected to uniform mapping of PT-RSs in the frequency domain asin the case of Embodiment 1. For example, in a case where there iscoordination among cells, the cells may use an interface between basestations (e.g. an X2 interface) to notify one another of information onsubcarriers over which to transmit PT-RSs.

In this way, whereas there is an increased possibility of collisionsbetween PT-RSs among the cells in a case where the cells do not shareinformation on subcarriers over which to transmit PT-RSs, subcarriersonto which to map PT-RSs can be surely varied among the cells in a casewhere there is coordination among the cells. This makes it possible toavoid collisions between PT-RSs among the cells.

In particular, in Embodiment 1, a spacing between PT-RSs in thefrequency domain in one cell is more likely to be identical to or aninteger multiple of a spacing between PT-RSs in the frequency domain inanother cell, and in a case where the mapping of PT-RSs is individuallydetermined in each cell, there is a higher possibility of simultaneouscollisions between PT-RSs over a plurality of subcarriers in each slot.Therefore, the application of the operation of Embodiment 1 tocoordinated cells makes it possible to reduce the possibility ofsimultaneous collisions between PT-RSs over a plurality of subcarriersand, as mentioned above, reduce the amount of calculation in thereceiver 200.

Embodiment 2

A transmitter and a receiver according to the present embodiment aredescribed with continued reference to FIGS. 4 and 5, as they areidentical in basic configuration to the transmitter 100 and the receiver200, respectively, according to Embodiment 1.

In the present embodiment, identical or different hopping offsets areapplied to PT-RSs that are mapped within the assigned band of the mobilestation. That is, whereas subcarriers onto which PT-RSs are mapped ineach slot are at regular spacings in Embodiment 1, subcarriers ontowhich PT-RSs are mapped in each slot are not necessarily at regularspacings (i.e. are at irregular spacings) in the present embodiment.

The following describes Operation Example 1 and Operation Example 2according to the present embodiment.

Operation Example 1

In Operation Example 1 according to the present embodiment, the wholeassigned band of the mobile station serves as candidates for subcarriersonto which PT-RSs hop. That is, in Operation Example 1, the transmitter100 performs frequency hopping in the whole assigned band of the mobilestation and maps a plurality of PT-RSs onto any subcarriers,respectively, within the assigned band.

For example, the transmitter 100 (hopping pattern generator 102) and thereceiver 200 (hopping pattern generator 203) determine the initialpositions of PT-RSs and hopping offsets in the following way.

The following assumes that the size of the assigned band of the mobilestation is “N_(UE_BW) [RB]” and the density of allocation in thefrequency domain of PT-RSs that are mapped to the mobile station is “oneper N_(density) [RB]”. In this case, N_(UE_BW)/N_(density) PT-RSs areallocated in each slot. In this example, an index i of [0, 1, 2, . . . ,N_(UE_BW)/N_(density)−1] is attached to all of the N_(UE_BW)/N_(density)PT-RSs.

First, a method is described by which to determine the frequencypositions of PT-RSs (i.e. the initial positions of PT-RSs) in the firstslot in a frame onto which the PT-RSs are allocated.

The transmitter 100 selects one subcarrier as an initial position fromamong N_(UE_BW) RBs (1 RB=12 subcarriers here) assigned to the mobilestation and maps a PT-RS onto the subcarrier in the initial positionthus selected. In selecting an initial position (subcarrier), thetransmitter 100 uses a pseudo-random number function, at least one of“the cell ID, the group ID, and the UE ID”, and a PT-RS index i. Thisallows as different subcarriers as possible to be selected amongdifferent cells, different groups, different mobile stations, ordifferent PT-RSs (indices i).

Next, in the same way, the transmitter 100 selects another subcarrier asan initial position from among the N_(UE_BW) RBs assigned to the mobilestation and maps a PT-RS onto the subcarrier in the initial positionthus selected. The transmitter 100 repeats the same process until PT-RSsare mapped onto N_(UE_BW)/N_(density) subcarriers.

Thus, in Operation Example 1 of the present embodiment, the initialpositions (subcarriers) of a plurality of PT-RSs within the assignedband of the mobile station are not necessarily at regular spacings butare at irregular spacings. That is, initial positions onto which PT-RSsare mapped may be at irregular spacings.

Next, a method is described by which to determine hopping offsetsagainst PT-RSs in the second and subsequent slots.

The transmitter 100 selects one hopping offset from among [0, 1, 2, . .. , 12N_(UE_BW)−1] for each of the N_(UE_BW)/N_(density) PT-RSsallocated within one slot and subjects the PT-RS to hopping by using thevalue thus selected. It should be noted that in selecting a hoppingoffset, the transmitter 100 uses a pseudo-random number function, atleast one of “the cell ID, the group ID, and the UE ID”, a PT-RS indexi, and a slot number. This allows as different hopping offsets aspossible to be selected among different cells, different groups,different mobile stations, different PT-RSs, or different slots.

Further, through a process which is similar to that of theaforementioned transmitter 100, the receiver 200 identifies hoppingpatterns (initial positions and hopping offsets) and identifiessubcarrier positions onto which PT-RSs transmitted from the transmitter100 are mapped.

FIG. 9 shows an example of mapping of PT-RSs according to OperationExample 1 of the present embodiment.

In FIG. 9, the density of allocation of PT-RSs in the frequency domainis “one per RB” (i.e. N_(density)=1). Further, the assigned band(=N_(UE_BW)) of the mobile station consists of two RBs. Therefore, ineach slot, PT-RSs are mapped onto two subcarriers. Further, frequencyhopping of the PT-RSs is performed at the boundary between slots.

As shown in FIG. 9, the initial positions of the PT-RSs in Slot #0 arethe same subcarriers (ninth subcarriers of each separate RB) in the twoRBs within the assigned band. It should be noted that the initialpositions of PT-RSs are not necessarily the same subcarrier positions ineach separate RB within the assigned band.

Further, as shown in FIG. 9, one of the PT-RSs is subjected to a hoppingoffset of 2 subcarriers, and the other PT-RS is subjected to a hoppingoffset of 10 subcarriers. That is, different hopping offsets are setagainst each separate PT-RS. As a result, as shown in FIG. 9, in Slot#1, the PT-RSs are mapped onto subcarriers located two subcarriers andten subcarriers, respectively, away from the subcarriers onto which thePT-RSs were mapped in each separate RB of Slot #0. In FIG. 9, in Slot#1, the two PT-RSs are mapped on one of the RBs of the assigned band ofthe mobile station and no PT-RSs are mapped on the other RB. Thus, thePT-RSs are irregularly mapped in the frequency domain.

In Operation Example 1, hopping offsets are set against a plurality ofPT-RSs (in FIG. 9, two PT-RSs) that are mapped in each slot. For thisreason, in Operation Example 1, unlike in Embodiment 1 (FIG. 8), hoppingoffsets are not necessarily identical against all PT-RSs. As a result,as shown in FIG. 9, there is a case where PT-RSs are intensively mappedonto one RB and no PT-RSs are mapped onto another RB. Note, however,that in this case, too, the density of PT-RSs in the assigned band as awhole remains “one per RB”.

Thus, in Operation Example 1, in which hopping patterns (initialpositions, hopping offsets) are determined against each separate PT-RS,hopping of each PT-RS is high in degree of freedom, so that there isincreased randomness of interference.

Although Operation Example 1 (FIG. 9) has illustrated a case where thenumber of PT-RS antenna ports is 1, the number of PT-RS antenna portsmay be 2 or larger. In a case where the number of PT-RS antenna ports ismore than one, the transmitter 100 may for example select the initialpositions of PT-RSs so that the PT-RSs are mapped onto differentsubcarriers according to antenna port numbers in addition to “the cellID, the group ID, or the UE ID” and the PT-RS index i. Note, however,that hopping offsets against PT-RSs that are transmitted from theplurality of antenna ports, respectively, take on identical values. Thisis intended to avoid the occurrence of a collision between PT-RS portsdue to frequency hopping.

Operation Example 2

In Operation Example 2 according to the present embodiment, candidatesfor subcarriers onto which PT-RSs hop are confined to a limited band.This limited band is hereinafter referred to a “PT-RS sub-band”. Thebandwidth of a PT-RS sub-band may be set according to the setting of thedensity of allocation of PT-RSs in the frequency domain so that a PT-RSis mapped onto only one subcarrier in the PT-RS sub-band.

For example, the transmitter 100 (hopping pattern generator 102) and thereceiver 200 (hopping pattern generator 203) determine the initialpositions of PT-RSs and hopping offsets in the following way.

The following assumes that the size of the assigned band of the mobilestation is “N_(UE_BW) [RB]” and the density of allocation in thefrequency domain of PT-RSs that are mapped to the mobile station is “oneper N_(density) [RB]”. In this case, N_(UE_BW)/N_(density) PT-RSs areallocated in each slot.

Further, the transmitter 100 divides N_(UE_BW) RBs into groups ofcontiguous N_(density) RBs. One group is referred to as “PT-RSsub-band”.

First, a method is described by which to determine the frequencypositions of PT-RSs (i.e. the initial positions of PT-RSs) in the firstslot in a frame onto which the PT-RSs are allocated.

The transmitter 100 selects one subcarrier as an initial position fromwithin a certain PT-RS sub-band of the first slot and maps a PT-RS ontothe subcarrier in the initial position thus selected. In selecting aninitial position (subcarrier), the transmitter 100 uses a pseudo-randomnumber function, at least one of “the cell ID, the group ID, and the UEID”, and a PT-RS sub-band index. This allows as different subcarriers aspossible to be selected among different cells, different groups,different mobile stations, or different PT-RS sub-bands.

The transmitter 100 repeats the initial position setting process on allPT-RS sub-bands.

Next, a method is described by which to determine hopping offsetsagainst PT-RSs in the second and subsequent slots.

For each PT-RS sub-band, the transmitter 100 selects one subcarrier fromwithin the PT-RS sub-band as a hopping-destination subcarrier. Forexample, in selecting a subcarrier, the transmitter 100 uses apseudo-random number function, at least one of “the cell ID, the groupID, and the UE ID”, a PT-RS sub-band index, and a slot number. Thisallows as different subcarriers as possible to be selected amongdifferent cells, different groups, different mobile stations, differentPT-RS sub-bands, or different slots. That is, in each PT-RS sub-band,the difference between the index of a subcarrier selected in the currentslot and the index of a subcarrier onto which a PT-RS was mapped in theprevious slot serves as a hopping offset.

The transmitter 100 repeats the same subcarrier selecting process on allPT-RS sub-bands.

Further, through a process which is similar to that of theaforementioned transmitter 100, the receiver 200 identifies, for eachPT-RS sub-band, a subcarrier position onto which a PT-RS is mapped ineach slot.

FIG. 10 shows an example of mapping of PT-RSs according to OperationExample 2 of the present embodiment.

In FIG. 10, the density of allocation of PT-RSs in the frequency domainis “one per RB” (i.e. N_(density)=1). Further, in FIG. 10, the assignedband of the mobile station is divided into PT-RS sub-bands (includingPT-RS sub-bands #0 and #1) for each separate RB. Further, frequencyhopping of the PT-RSs is performed at the boundary between slots.

In FIG. 10, the initial positions of the PT-RSs in Slot #0 are selectedin each separate PT-RS sub-band. Further, in FIG. 10, as the mappingpositions of the PT-RSs in Slot #1, any one subcarrier within each PT-RSsub-band is selected. That is, as shown in FIG. 10, the PT-RS mapped inSlot #0 in PT-RS sub-band #0 does not hop into PT-RS sub-band #1 in Slot#1 but hops onto a subcarrier within PT-RS sub-band #0. The same appliesto the PT-RS within PT-RS sub-band #1.

Further, in FIG. 10, unlike in Embodiment 1 (FIG. 8), hopping offsetsare not necessarily identical against all PT-RSs, and the frequencyspacings between PT-RSs are not uniform.

Thus, in Operation Example 2, the transmitter 100 maps any one of aplurality of PT-RSs onto a corresponding one of a plurality of PT-RSsub-bands (partial bands) and performs frequency hopping on each PT-RSwithin the corresponding PT-RS sub-band. As a result, since hoppingpatterns (initial positons, hopping offsets) are determined against eachseparate PT-RS, hopping of each PT-RS is high in degree of freedom, sothat there is increased randomness of interference.

Further, in Operation Example 2, each PT-RS hops within a PT-RSsub-band. That is, in Operation Example 2, frequency hopping of a PT-RSis confined in a PT-RS sub-band, and in any slot, a PT-RS is mappedwithin each PT-RS sub-band. For this reason, all PT-RSs avoid beingmapped onto adjacent subcarriers and become robust against frequencyselectivity.

Although Operation Example 2 (FIG. 10) has illustrated a case where thenumber of PT-RS antenna ports is 1, the number of PT-RS antenna portsmay be 2 or larger. In a case where the number of PT-RS antenna ports ismore than one, the transmitter 100 may for example select the initialpositions of PT-RSs so that the PT-RSs are mapped onto differentsubcarriers according to antenna port numbers in addition to “the cellID, the group ID, or the UE ID” and the PT-RS sub-band index. Note,however, that hopping offsets against PT-RSs that are transmitted fromthe plurality of antenna ports, respectively, take on identical values.This is intended to avoid the occurrence of a collision between PT-RSports due to frequency hopping.

The foregoing has described Operation Examples 1 and 2 of the presentembodiment.

Thus, in the present embodiment, in which PT-RSs are irregularlyallocated in the frequency domain, combinations of a pluralitysubcarriers onto which a plurality of PT-RSs that are transmitted at agiven time (e.g. in the same slot) are mapped are more likely to varyamong different cells, groups, or mobile stations. Therefore, amongdifferent cells, groups, or mobile stations, the possibility ofsimultaneous collisions between PT-RSs mapped onto a plurality ofsubcarriers can be reduced.

Further, according to the present embodiment, for example, even ifPT-RSs are mapped onto the same subcarriers among different cells,groups, or mobile stations in a certain slot (e.g. the first slot in aframe onto which the PT-RSs are mapped), the PT-RS are more likely to bemapped onto different subcarriers among different cells, groups, ormobile stations in another slot. Therefore, among different cells,groups, or mobile stations, the possibility of simultaneous collisionsbetween PT-RSs over a plurality of slots can be reduced.

Modification of Embodiment 2

It should be noted that in a case where there is no coordination amongcells and the cells do not share information as to how PT-RSs are mappedin each cell, these cells may be subjected to irregular mapping ofPT-RSs in the frequency domain as in the case of Embodiment 2.

In this way, whereas there is an increased possibility of collisionsbetween PT-RSs among the cells in a case where the cells do not shareinformation on subcarriers over which to transmit PT-RSs, irregularmapping of PT-RSs in the frequency domain as in the case of Embodiment 2increases the randomness of subcarriers onto which the PT-RSs are mappedin each cell, thus making it possible to reduce the possibility ofcollisions between PT-RSs simultaneously mapped onto a plurality ofsubcarriers among cells.

Modifications of Embodiments 1 and 2

Further, in a case where there is coordination among cells, a pluralityof PT-RSs that are transmitted at a given time (e.g. slot) may beuniformly mapped in the frequency domain as in the case of Embodiment 1,and in a case where there is no coordination among cells, a plurality ofPT-RSs that are transmitted at a given time may be irregularly mapped(at irregular spacings) in the frequency domain. Further, thetransmitter 100 may switch between the PT-RS mapping of Embodiment 1 andthe PT-RS mapping of Embodiment 2 according to the presence or absenceof coordination among cells.

It should be noted that in a case where there is coordination amongcells, the cells may use an interface between base stations (e.g. an X2interface) to notify one another of information on subcarriers overwhich to transmit PT-RSs.

By thus flexibly switching between the PT-RS mapping method according tothe situation of coordination among cells, PT-RSs can be mapped by anoptimum method in each situation. As a result, in a case where there iscoordination among cells and the mapping method of Embodiment 1 isapplied, the amount of calculation of the receiver 200 can be reduced.Further, in a case where there is no coordination among cells and themapping method of Embodiment 2 is applied, the possibility ofsimultaneous collisions of PT-RSs of a plurality of subcarriers can bereduced.

Embodiment 3

A transmitter and a receiver according to the present embodiment aredescribed with continued reference to FIGS. 4 and 5, as they areidentical in basic configuration to the transmitter 100 and the receiver200, respectively, according to Embodiment 1.

In the present embodiment, the transmitter 100 maps a PT-RS onto any ofsubcarriers on which DMRSs using the same precoding as the PT-RS aremapped. That is, the destination of hopping of a PT-RS is limited to thesame subcarrier as a DMRS sharing a precoding. That is, a PT-RS ispresent on a subcarrier on which a DMRS that is transmitted through thesame antenna port is present.

The following describes Operation Examples 1 to 3 according to thepresent embodiment. It should be noted that the PT-RS mapping methods ofOperation Examples 1 to 3 according to the present embodiment correspondto the operation example of Embodiment 1 (see FIG. 8), Operation Example1 of Embodiment 2 (see FIG. 9), and Operation Example 2 of Embodiment 2(see FIG. 10), respectively, and differ in that a subcarrier onto whicha PT-RS is mapped is limited to a subcarrier on which a DMRS of anidentical precoding is mapped.

Operation Example 1

According to Operation Example 1, in the first slot in a frame ontowhich PT-RSs are mapped, the PT-RSs are mapped at regular spacings in auniformly-distributed manner in the frequency domain, as is the casewith Operation Example 1 of Embodiment 1. Further, in a subsequent slotof the frame, identical hopping offsets are applied to all PT-RSs withinthe assigned band of the mobile station. That is, the transmitter 100performs frequency hopping on the PT-RSs so that subcarriers onto whichthe PT-RSs are mapped in each slot are uniformly distributed at regularspacings.

Note, however, that in Operation Example 1 according to the presentembodiment, a subcarrier onto which a PT-RS is mapped (including ahopping-destination subcarrier) is any of subcarriers on which DMRSssubject to the same precoding as the PT-RS are present.

For example, the transmitter 100 (hopping pattern generator 102) and thereceiver 200 (hopping pattern generator 203) determine the initialpositions of PT-RSs and hopping offsets in the following way.

The following assumes that the size of the assigned band of the mobilestation is “N_(UE_BW) [RB]” and the density of allocation in thefrequency domain of PT-RSs that are mapped to the mobile station is “oneper N_(density) [RB]”.

Further, it is assumed that PT-RSs are transmitted by the same precodingas DMRS Port Numbers 1 to N_(port). That is, PT-RSs are transmittedthrough N_(port) antenna ports.

First, a method is described by which to determine the frequencypositions of PT-RSs (i.e. the initial positions of PT-RSs) in the firstslot in a frame onto which the PT-RSs are allocated.

For example, the transmitter 100 maps, onto a subcarrier, a PT-RSsubject to the same precoding as DMRS Port Number 1. In so doing, thetransmitter 100 selects one subcarrier as an initial position from amongsubcarriers, included in N_(UE_BW) RBs (1 RB=12 subcarriers here)assigned to the mobile station, over which DMRSs of DMRS Port Number 1are transmitted and maps the PT-RS onto the subcarrier in the initialposition thus selected. In selecting an initial position (subcarrier),the transmitter 100 uses a pseudo-random number function and at leastone of “the cell ID, the group ID, and the UE ID”. This allows asdifferent subcarriers as possible to be selected among different cells,different groups, or different mobile stations.

Next, in an RB located N_(density) away from the RB on which theaforementioned PT-RS is allocated, the transmitter 100 maps a PT-RS ontothe same subcarrier as the subcarrier of the RB on which theaforementioned PT-RS is mapped (i.e. a subcarrier over which a DMRS ofDMRS Port Number 1 is transmitted). The transmitter 100 repeats thisprocess until PT-RSs are mapped onto N_(UE_BW)/N_(density) subcarriers(i.e. on all RBs onto which PT-RSs are mapped).

Further, upon completion of mapping of PT-RSs corresponding to DMRS PortNumber 1, the transmitter 100 maps PT-RSs of other DMRS Port Numbers 2to N_(port) onto subcarriers in the same way.

Next, a method is described by which to determine hopping offsetsagainst PT-RSs in the second and subsequent slots.

It is assumed here that a DMRS at one DMRS port is mapped everyN_(DMRS_Space) subcarriers.

The transmitter 100 selects one hopping offset from among [0,N_(DMRS_Space), 2N_(DMRS_Space), . . . ] against N_(UE_BW)/N_(density)PT-RSs of Antenna Port Number 1 and performs frequency hopping of all ofthe PT-RSs by using the value (hopping offset) thus selected. It shouldbe noted that in selecting a hopping offset, the transmitter 100 uses apseudo-random number function, at least one of “the cell ID, the groupID, and the UE ID”, and a slot number. This allows as different hoppingoffsets as possible to be selected among different cells, differentgroups, different mobile stations, or different slots.

Upon completion of frequency hopping of PT-RSs corresponding to AntennaPort Number 1, the transmitter 100 performs frequency hopping on PT-RSsof other Antenna Port Numbers 2 to N_(port) by using the hopping offsetused for Antenna Port Number 1.

Further, through a process which is similar to that of theaforementioned transmitter 100, the receiver 200 identifies hoppingpatterns (initial positions and hopping offsets) and identifiessubcarrier positions onto which PT-RSs transmitted from the transmitter100 are mapped.

FIG. 11 shows an example of mapping of PT-RSs according to OperationExample 1 of the present embodiment.

In FIG. 11, the density of allocation of PT-RSs in the frequency domainis “one per RB” (i.e. N_(density)=1). Therefore, in FIG. 11, in anyslot, a PT-RS is mapped on one subcarrier in every RB of the assignedband of the mobile station. Further, N_(DMRS_Space) equals 4subcarriers. Further, frequency hopping of the PT-RSs is performed atthe boundary between slots.

Further, although FIG. 11 illustrates an example of mapping of PT-RSs ofAntenna Port Number 1, PT-RSs of other antenna port numbers may bemapped in the same way.

As shown in FIG. 11, the initial position of each PT-RS of Antenna PortNumber 1 in Slot #0 is one (fourth subcarrier of each RB) of subcarrierscorresponding to DMRS Port Number 1. Further, as shown in FIG. 11, thehopping offset consists of four subcarriers. Therefore, in Slot #1, aPT-RS is mapped onto a subcarrier (eighth subcarrier of each RB) locatedfour subcarriers away from the subcarrier onto which the PT-RS wasmapped in each RB of Slot #0. It should be noted that the hopping offsetis not limited to four subcarriers shown in FIG. 11 but needs only beselected from among 0, 4, 8, . . . , which are integer multiples ofN_(DMRS_Space).

That is, as shown in FIG. 11, in each slot including the first andsubsequent slots, frequency spacings between PT-RSs are uniformly thesame (in FIG. 11, one RB (twelve subcarriers). As a result, subcarriersonto which the PT-RSs are mapped are uniformly distributed at regularspacings in each slot, so that the PT-RSs become robust against thefrequency selectivity of channels.

Further, in FIG. 11, unlike in Embodiment 1 (FIG. 8), a PT-RS of AntennaPort Number 1 is mapped onto a subcarrier on which a DMRS of the sameport (DMRS Port Number 1) is present. That is, a PT-RS of Antenna PortNumber 1 (Port 1) may be allocated onto an RE of a subcarrier on which aDMRS of Antenna Port Number 1 is present (see FIG. 11).

Operation Example 2

In Operation Example 2 according to the present embodiment, the wholeassigned band of the mobile station serves as candidates for subcarriersonto which PT-RSs hop, as is the case with Operation Example 1 ofEmbodiment 2. That is, in Operation Example 2, the transmitter 100performs frequency hopping in the whole assigned band of the mobilestation and maps a plurality of PT-RSs onto any subcarriers,respectively, within the assigned band.

Note, however, that in Operation Example 2 according to the presentembodiment, a subcarrier onto which a PT-RS is mapped (including ahopping-destination subcarrier) is any of subcarriers on which DMRSssubject to the same precoding as the PT-RS are present.

For example, the transmitter 100 (hopping pattern generator 102) and thereceiver 200 (hopping pattern generator 203) determine the initialpositions of PT-RSs and hopping offsets in the following way.

The following assumes that the size of the assigned band of the mobilestation is “N_(UE_BW) [RB]” and the density of allocation in thefrequency domain of PT-RSs that are mapped to the mobile station is “oneper N_(density) [RB]”. In this case, N_(UE_BW)/N_(density) PT-RSs areallocated in each slot. In this example, an index i of [0, 1, 2, . . . ,N_(UE_BW)/N_(density)−1] is attached to all of the N_(UE_BW)/N_(density)PT-RSs.

Further, it is assumed that PT-RSs are transmitted by the same precodingas DMRS Port Numbers 1 to N_(port). That is, PT-RSs are transmittedthrough N_(port) antenna ports.

First, a method is described by which to determine the frequencypositions of PT-RSs (i.e. the initial positions of PT-RSs) in the firstslot in a frame onto which the PT-RSs are allocated.

For example, the transmitter 100 maps, onto a subcarrier, a PT-RSsubject to the same precoding as DMRS Port Number 1. In so doing, thetransmitter 100 selects one subcarrier as an initial position from amongsubcarriers, included in N_(UE_BW) RBs (1 RB=12 subcarriers here)assigned to the mobile station, over which DMRSs of DMRS Port Number 1are transmitted and maps the PT-RS onto the subcarrier in the initialposition thus selected. In selecting an initial position (subcarrier),the transmitter 100 uses a pseudo-random number function, at least oneof “the cell ID, the group ID, and the UE ID”, and a PT-RS index i. Thisallows as different subcarriers as possible to be selected amongdifferent cells, different groups, different mobile stations, ordifferent PT-RSs.

Next, in the same way, the transmitter 100 selects another subcarrier asthe initial position of a PT-RS of Antenna Port Number 1 from among theN_(UE_BW) RBs assigned to the mobile station and maps the PT-RS onto thesubcarrier in the initial position thus selected. The transmitter 100repeats the same process until PT-RSs are mapped ontoN_(UE_BW)/N_(density) subcarriers.

Further, upon completion of mapping of PT-RSs corresponding to DMRS PortNumber 1, the transmitter 100 maps PT-RSs of other DMRS Port Numbers 2to N_(port) onto subcarriers in the same way.

Thus, in Operation Example 2, the initial positions (subcarriers) of aplurality of PT-RSs within the assigned band of the mobile station arenot necessarily at regular spacings but are at irregular spacings. Thatis, initial positions onto which PT-RSs are mapped may be at irregularspacings.

Next, a method is described by which to determine hopping offsetsagainst PT-RSs in the second and subsequent slots.

It is assumed here that a DMRS at one DMRS port is mapped everyN_(DMRS_Space) subcarriers.

The transmitter 100 selects one hopping offset from among [0,N_(DMRS_Space), 2N_(DMRS_Space), . . . ] for each of theN_(UE_BW)/N_(density) PT-RSs of Antenna Port Number 1 that are mappedwithin one slot and subjects the PT-RS to hopping by using the valuethus selected. It should be noted that a hopping offset that is selectedfor each PT-RS may be a different value. It should be noted that inselecting a hopping offset, the transmitter 100 uses a pseudo-randomnumber function, at least one of “the cell ID, the group ID, and the UEID”, a PT-RS index i, and a slot number. This allows as differenthopping offsets as possible to be selected among different cells,different groups, different mobile stations, different PT-RSs, ordifferent slots.

Upon completion of frequency hopping of PT-RSs corresponding to AntennaPort Number 1, the transmitter 100 performs frequency hopping on PT-RSsof other Antenna Port Numbers 2 to N_(port) by using the hopping offsetused for Antenna Port Number 1.

Further, through a process which is similar to that of theaforementioned transmitter 100, the receiver 200 identifies hoppingpatterns (initial positions and hopping offsets) and identifiessubcarrier positions onto which PT-RSs transmitted from the transmitter100 are mapped.

FIG. 12 shows an example of mapping of PT-RSs according to OperationExample 2 of the present embodiment.

In FIG. 12, the density of allocation of PT-RSs in the frequency domainis “one per RB” (i.e. N_(density)=1). Further, the assigned band(=N_(UE_BW)) of the mobile station consists of two RBs. Therefore, ineach slot, PT-RSs are mapped onto two subcarriers. Further, frequencyhopping of the PT-RSs is performed at the boundary between slots.

Further, although FIG. 12 illustrates an example of mapping of PT-RSs ofAntenna Port Number 1, PT-RSs of other antenna port numbers may bemapped in the same way.

In FIG. 12, the initial position of each PT-RS of Antenna Port Number 1in Slot #0 is one of subcarriers corresponding to DMRS Port Number 1.That is, a PT-RS of Antenna Port Number 1 (Port 1) shown in FIG. 12 maybe allocated onto an RE of a subcarrier on which a DMRS of Antenna PortNumber 1 is present. As shown in FIG. 12, in Slot #0, PT-RSs are mappedonto the same subcarriers (eighth subcarriers of each separate RB) inthe two RBs within the assigned band, respectively. Note, however, thatthe initial positions of the PT-RSs are not necessarily the samesubcarrier positions in each separate RB within the assigned band butmay be different.

Further, as shown in FIG. 12, one of the PT-RSs is subjected to ahopping offset of 4 subcarriers, which is an integer multiple (singletime) of the subcarrier spacing N_(DMRS_Space) of DMRS Port Number 1,and the other PT-RS is subjected to a hopping offset of 8 subcarriers,which is an integer multiple (two times) of the subcarrier spacingN_(DMRS_Space). That is, different hopping offsets are set against eachseparate PT-RS. In FIG. 12, in Slot #1, the two PT-RSs are mapped on oneof the RBs of the assigned band of the mobile station and no PT-RSs aremapped on the other RB. Thus, the PT-RSs are irregularly mapped in thefrequency domain.

Thus, in Operation Example 2, in which hopping patterns (initialpositions, hopping offsets) are determined against each separate PT-RS,hopping of each PT-RS is high in degree of freedom, so that there isincreased randomness of interference.

Operation Example 3

In Operation Example 3 according to the present embodiment, candidatesfor subcarriers onto which PT-RSs hop are confined to a limited band(PT-RS sub-band), as is the case with Operation Example 2 of Embodiment2. The bandwidth of a PT-RS sub-band may be set according to the settingof the density of allocation of PT-RSs in the frequency domain so that aPT-RS is mapped onto only one subcarrier in the PT-RS sub-band.

Note, however, that in Operation Example 3 according to the presentembodiment, a subcarrier onto which a PT-RS is mapped (including ahopping-destination subcarrier) is any of subcarriers on which DMRSssubject to the same precoding as the PT-RS are present.

For example, the transmitter 100 (hopping pattern generator 102) and thereceiver 200 (hopping pattern generator 203) determine the initialpositions of PT-RSs and hopping offsets in the following way.

The following assumes that the size of the assigned band of the mobilestation is “N_(UE_BW) [RB]” and the density of allocation in thefrequency domain of PT-RSs that are mapped to the mobile station is “oneper N_(density) [RB]”. In this case, N_(UE_BW)/N_(density) PT-RSs areallocated in each slot.

Further, it is assumed that PT-RSs are transmitted by the same precodingas DMRS Port Numbers 1 to N_(port). That is, PT-RSs are transmittedthrough N_(port) antenna ports. It is also assumed that a DMRS at oneDMRS port is mapped every N_(DMRS_Space) subcarriers.

Further, the transmitter 100 divides N_(UE_BW) RBs into groups (PT-RSsub-bands) of contiguous N_(density) RBs.

First, a method is described by which to determine the frequencypositions of PT-RSs (i.e. the initial positions of PT-RSs) in the firstslot in a frame onto which the PT-RSs are allocated.

The transmitter 100 selects one subcarrier as an initial position fromamong subcarriers in a certain PT-RS sub-band of the first slot overwhich DMRSs of DMRS Port Number 1 are transmitted and maps a PT-RS ontothe subcarrier in the initial position thus selected. In selecting aninitial position (subcarrier), the transmitter 100 uses a pseudo-randomnumber function, at least one of “the cell ID, the group ID, and the UEID”, a PT-RS sub-band index, and antenna port number. This allows asdifferent subcarriers as possible to be selected among different cells,different groups, different mobile stations, different PT-RS sub-bands,or different antenna ports.

The transmitter 100 repeats the initial position setting process on allPT-RS sub-bands.

Further, upon completion of mapping of PT-RSs corresponding to DMRS PortNumber 1, the transmitter 100 maps PT-RSs of other DMRS Port Numbers 2to N_(port) onto subcarriers in the same way.

The following illustrates a specific example of calculation of theinitial position of a PT-RS. It is assumed here that t₀ is the number ofthe first slot in which a PT-RS is mapped. A PT-RS of an antenna port pis mapped into the sth PT-RS sub-band in a slot t₀. Within this PT-RSsub-band, the number of subcarriers onto which the PT-RS can be mappedis 12 N_(density)/N_(DMRS_Space). Of the indices of these subcarriers,the smallest number is k₀ ^(p,s). The index F_(init)(s, p, t₀) of asubcarrier onto which to map the PT-RS may be obtained according toFormula (1):

$\begin{matrix}{\mspace{79mu}\lbrack {{Math}.\mspace{14mu} 1} \rbrack} & \; \\{{F_{init}( {s,p,t_{0}} )} = {k_{0}^{p,s} + {\{ {( {\sum\limits_{k = {{10s} + 1}}^{{10s} + 9}{{c(k)} \times 2^{k - {({{10s} + 1})}}}} )\;{{mod}( {12 \times \frac{N_{density}}{N_{DMRS\_ Space}}} )}} \} \times N_{DMRS\_ Space}}}} & (1)\end{matrix}$

It should be noted that the pseudo-random number function c(k) used maybe a function described in 3GPP Standard 36.211 “7.2 Pseudo-randomsequence generation”. This function may be initialized byc_(init)=100N_(ID)+p. Note here that N_(ID) may be the cell ID, thegroup ID, the UE ID, or a value obtained by a combination thereof.

Next, a method is described by which to determine hopping offsetsagainst PT-RSs in the second and subsequent slots.

For each PT-RS sub-band, the transmitter 100 selects, as ahopping-destination subcarrier, a subcarrier in the PT-RS sub-band overwhich a DMRS of DMRS Port Number 1 is transmitted. For example, inselecting a subcarrier, the transmitter 100 uses a pseudo-random numberfunction, at least one of “the cell ID, the group ID, and the UE ID”, aPT-RS sub-band index, a slot number, and an antenna port number. Thisallows as different subcarriers as possible to be selected amongdifferent cells, different groups, different mobile stations, differentPT-RS sub-bands, different slots, or different antenna ports. That is,in each PT-RS sub-band, the difference between the index of a subcarrierselected in the current slot and the index of a subcarrier onto which aPT-RS was mapped in the previous slot serves as a hopping offset.

The transmitter 100 repeats the same subcarrier selecting process on allPT-RS sub-bands.

The following illustrates a specific example of calculation of a hoppingoffset of a PT-RS. The index F(s, p, t) of a subcarrier onto which aPT-RS is mapped in a slot t following the first slot t₀ may be obtainedaccording to Formula (2):

$\begin{matrix}{\mspace{79mu}\lbrack {{Math}.\mspace{14mu} 2} \rbrack} & \; \\{{F( {s,p,t} )} = {k_{0}^{p,s} + {\{ {( {\sum\limits_{k = {{10t} + 1}}^{{10t} + 9}{{c(k)} \times 2^{k - {({{10t} + 1})}}}} )\;{{mod}( {12 \times \frac{N_{density}}{N_{DMRS\_ Space}}} )}} \} \times N_{DMRS\_ Space}}}} & (2)\end{matrix}$

Further, the pseudo-random number function c(k) may be initialized byc_(init)=10000N_(ID)+100S-+p. Note here that N_(ID) may be the cell ID,the group ID, the UE ID, or a value obtained by a combination thereof.Therefore, the hopping offset F_(hop)(s, p, t) from the slot t−1 to theslot t is determined by Formula (3):[Math. 3]F _(hop)(s, p, t)=F(s, p, t)−F(s, p, t−1)  (3)

Further, through a process which is similar to that of theaforementioned transmitter 100, the receiver 200 identifies, for eachPT-RS sub-band, a subcarrier position onto which a PT-RS is mapped ineach slot.

FIG. 13 shows an example of mapping of PT-RSs according to OperationExample 3 of the present embodiment.

In FIG. 13, the density of allocation of PT-RSs in the frequency domainis “one per RB” (i.e. N_(density)=1). Further, in FIG. 13, the assignedband of the mobile station is divided into PT-RS sub-bands (includingPT-RS sub-bands #0 and #1) for each separate RB. Further, the spacing(=N_(DMRS_Space)) between DMRSs of the same antenna port number is 4subcarriers. Further, frequency hopping of the PT-RSs is performed atthe boundary between slots.

Further, although FIG. 13 illustrates an example of mapping of PT-RSs ofAntenna Port Number 1, PT-RSs of other antenna port numbers may bemapped in the same way. That is, a PT-RS of Antenna Port Number 1(Port 1) shown in FIG. 13 may be allocated onto an RE of a subcarrier onwhich a DMRS of Antenna Port Number 1 is present.

In FIG. 13, the initial position of each of the PT-RSs in Slot #0 iscalculated according to both the smallest number k₀ ^(p,s)(k₀ ^(1,0), k₀^(1,1)) of the indices of subcarriers onto which PT-RSs of the antennaport number p=1 can be mapped in a corresponding one of PT-RS sub-bands#0 and #1 and Formula (1). Further, in FIG. 13, as the mapping positionsof the PT-RSs in Slot #1, any one subcarrier within each PT-RS sub-bandis selected. For example, the mapping position F(s, 1, 1) of each of thePT-RSs of Antenna Port Number 1 (p=1) in Slot #1 (t=1) within thecorresponding one of PT-RS sub-bands #0 and #1 (i.e. s=0, 1) may becalculated according to Formula (2).

That is, as shown in FIG. 13, the PT-RS mapped in Slot #0 in PT-RSsub-band #0 does not hop into PT-RS sub-band #1 in Slot #1 but hops ontoa subcarrier within PT-RS sub-band #0. The same applies to the PT-RSwithin PT-RS sub-band #1.

Further, in FIG. 13, unlike in Embodiment 1 (FIG. 8), hopping offsetsare not necessarily identical against all PT-RSs, and the frequencyspacings between PT-RSs are not uniform.

Thus, in Operation Example 3, the transmitter 100 maps any one of aplurality of PT-RSs onto a corresponding one of a plurality of PT-RSsub-bands (partial bands) and performs frequency hopping on each PT-RSwithin the corresponding PT-RS sub-band. As a result, since hoppingpatterns (initial positons, hopping offsets) are determined against eachseparate PT-RS, hopping of each PT-RS is high in degree of freedom, sothat there is increased randomness of interference. Further, inOperation Example 3, each PT-RS hops within a PT-RS sub-band. For thisreason, all PT-RSs avoid being mapped onto adjacent subcarriers andbecome robust against frequency selectivity.

The foregoing has described Operation Examples 1 to 3 of the presentembodiment.

Thus, in the present embodiment, a subcarrier onto which a PT-RS ismapped is limited to a subcarrier on which a DMRS using the sameprecoding as the PT-RS is present. This makes it possible to increasethe precision of a CPE/ICI correction in a case where it is assumed thatthe same spatial channel is used for the DMRS and the PT-RS. Further,since subcarriers onto which PT-RSs can be mapped vary according toantenna port, mapping of PT-RSs of different antenna ports onto the samesubcarrier can be avoided.

In Embodiment 3, in a case where subcarriers on which PT-RSs can bepresent vary from antenna port to antenna port, PT-RSs that aretransmitted through different antenna ports are not mapped onto the samesubcarrier, so that there is no need to have identical hopping offsetsamong different antenna ports. Note, however, that even in a case wheresubcarriers onto which PT-RSs can be mapped overlap as in the case ofAntenna Ports 1 and 5 shown in FIG. 13, PT-RS Ports 1 and 5 do not needto be multiplexed onto the same subcarrier but may be mapped ontodifferent subcarriers.

The foregoing has described each embodiment of the present disclosure.

It should be noted that in the embodiments described above, at least oneof “a cell ID, a group ID, and a UE ID” and a slot number may becombined for the determination of the initial positions of PT-RSs in thefirst slot and hopping offsets.

Further, the time-domain index, which is used for the determination ofhopping offsets of PT-RSs, does not need to be a symbol number but maybe a slot number, a minislot number, a subframe number, a frame number,or a value obtained by a combination thereof.

Further, the temporal period (interval) of frequency hopping may be setto “every symbol”, “every two symbols”, “every specified number ofsymbols”, “every slot”, “every minislot”, “every subframe”, or the like.For example, a short interval of frequency hopping leads to an increasein randomizedness of interference caused by a collision between PT-RSs,and a long interval of frequency hopping makes it possible to reduce thefrequency at which the receiver 200 identifies (calculates) thepositions of PT-RSs. Further, the timing of frequency hopping is notlimited to the boundary between slots.

Further, the time period of hopping of PT-RSs may be set in combinationwith the unit of assignment of data. When the unit of assignment of datais a slot, hopping of PT-RSs may be set in a slot unit, too, and whenthe unit of assignment of data is a minislot, hopping of PT-RSs is setin a minislot unit, too.

Further, even when the unit of assignment of data is a minislot, hoppingof PT-RSs may be set in a slot unit. This is because it is conceivablethat the unit of assignment of data may be different for each cell. Inorder to make cells uniform in period of hopping of PT-RSs, the unit ofhopping of PT-RSs is set regardless of the unit of assignment of data.

Further, although the embodiments (FIGS. 8 to 13) described above assumethat the length of a slot is 14 symbols, the length of a slot is notlimited to 14 symbols. For example, the same frequency hopping may beapplied even when the length of a slot is 7 symbols. Further, althougheach of the drawings shows the positions of the REs of DMRSs that aremapped at their respective antenna ports, this is merely an example andis not intended to impose any limitation. Further, DMRSs of differentantenna ports may be subjected to CDM (code division multiplexing).

Further, in the case of frequency multiplexing of control channels(PDCCH (Physical Downlink Control Channel) and PUCCH (Physical UplinkControl Channel)) and data channels (PDSCH (Physical Downlink SharedChannel) and PUSCH (Physical Uplink Shared Channel)), PT-RSs may bemapped onto their symbols.

Further, the term “CPE/ICI correction” used in the embodiments describedabove means “correcting a CPE”, “correcting ICI”, or “correcting both aCPE and ICI”.

Further, in the embodiments described above, the phase noise may begenerated from a local generator of the receiver as well as the localoscillator of the transmitter.

Further, the initial positions of PT-RSs, the hopping offsets, theassigned band N_(UE_BW) [RB], the density of allocation in the frequencydomain “one per N_(density) [RB]”, the frequency spacing N_(DMRS_Space)between DMRS ports, and other parameters used in each of the operationexamples of the embodiments described above are merely examples and arenot limited to these values.

Further, in each of the operation examples of the embodiments describedabove, the method for setting the frequency positions of PT-RSs does notneed to be on a subcarrier-by-subcarrier basis but may be on an RB-by-RBbasis. For example, the initial positions of PT-RSs may be expressed onan RB-by-RB basis, and the position of such an RB may be calculated andselected using a pseudo-random number function, various types of index,and the like. At this time, the spacings between RBs at which PT-RSs aremapped may be regular spacings or irregular spacings. Furthermore, ahopping offset may be set on an RB-by-RB basis, and this value may becalculated and selected using a pseudo-random number function, varioustypes of index, and the like. In each RB onto which a PT-RS is mapped, arelative subcarrier position onto which the PT-RS is mapped may be apreset value, a value notified from a higher layer or the like, or avalue calculated using a pseudo-random number function, various types ofindex, and the like.

Further, the present disclosure may be achieved with software, hardware,or software in cooperation with hardware. Each of the functional blocksused to describe the embodiments above may be partly or wholly achievedas an LSI, which is an integrated circuit, and each of the processesdescribed in the embodiments above may be partly or wholly controlled bya single LSI or a combination of LSIs. The LSIs may each be composed ofindividual chips, or may be composed of a single chip so as to includesome or all of the functional blocks. The LSIs may each include an inputand an output for data. Depending on the degree of integration, the LSIsmay alternatively be referred to as “ICs”, “system LSIs”, “super LSIs”,or “ultra LSIs”. However, the technique of implementing an integratedcircuit is not limited to LSI and may be achieved by using a dedicatedcircuit, a general-purpose processor, or a dedicated processor. Inaddition, an FPGA (field-programmable gate array) that can be programmedafter the manufacture of an LSI or a reconfigurable processor in whichthe connections and the settings of circuit cells disposed inside an LSIcan be reconfigured may be used. The present disclosure may be achievedas digital processing or analog processing. If future integrated circuittechnology replaces LSI as a result of the advancement of semiconductortechnology or other derivative technology, the functional blocks couldbe integrated using the future integrated circuit technology. Forexample, biotechnology can also be applied.

A transmitter of the present disclosure includes an assignment circuitthat maps a phase tracking reference signal onto a subcarrier and atransmitting circuit that transmits a signal containing the phasetracking reference signal. The phase tracking reference signal is mappedonto a different subcarrier for each cell, group, or mobile station.

In the transmitter of the present disclosure, the phase trackingreference signal is mapped onto a subcarrier determined by using eitheran index for identification of the cell, group, or mobile station orhigher layer signaling.

In the transmitter of the present disclosure, the phase trackingreference signal is subjected to frequency hopping every unit time.

In the transmitter of the present disclosure, the phase trackingreference signal is subjected to a hopping offset determined by usingeither an index for identification of the cell, group, or mobile stationor a time-domain index.

In the transmitter of the present disclosure, the time-domain index is asymbol number, a slot number, a minislot number, a subframe number, or aframe number.

In the transmitter of the present disclosure, a plurality of the hoppingoffsets against a plurality of the phase tracking reference signals thatare transmitted from a plurality of antenna ports, respectively, areidentical.

In the transmitter of the present disclosure, the assignment circuitmaps, at regular spacings in a frequency domain, a plurality of thephase tracking reference signals transmitted at a given time.

In the transmitter of the present disclosure, the assignment circuitmaps, at irregular spacings in a frequency domain, a plurality of thephase tracking reference signals transmitted at a given time.

In the transmitter of the present disclosure, the assignment circuitperforms frequency hopping in a whole band assigned to the mobilestation and maps the plurality of phase tracking reference signals ontoany subcarriers within the band.

In the transmitter of the present disclosure, the mobile station isassigned a band divided into a plurality of partial bands, theassignment circuit maps any one of the plurality of phase trackingreference signals onto a corresponding one of the plurality of partialbands and performs frequency hopping on the phase tracking referencesignal within the corresponding partial band.

In the transmitter of the present disclosure, in a case where there iscoordination among cells, the assignment circuit maps, at regularspacings in a frequency domain, a plurality of the phase trackingreference signals that are transmitted at a given time and, in a casewhere there is no coordination among the cells, maps the plurality ofphase tracking reference signals at irregular spacings in the frequencydomain.

In the transmitter of the present disclosure, the assignment circuitmaps the phase tracking reference signal onto any of subcarriers onwhich demodulating reference signals using a precoding which isidentical to that used by the phase tracking reference signal aremapped.

A receiver of the present disclosure includes a receiving circuit thatreceives a signal containing a phase tracking reference signal and ademodulating circuit that demodulates a data signal by using a phasenoise estimated value calculated using the phase tracking referencesignal. The phase tracking reference signal is mapped onto a differentsubcarrier for each cell, group, or mobile station.

A transmission method of the present disclosure includes mapping a phasetracking reference signal onto a subcarrier and transmitting a signalcontaining the phase tracking reference signal. The phase trackingreference signal is mapped onto a different subcarrier for each cell,group, or mobile station.

A reception method of the present disclosure includes receiving a signalcontaining a phase tracking reference signal and demodulating a datasignal by using a phase noise estimated value calculated using the phasetracking reference signal. The phase tracking reference signal is mappedonto a different subcarrier for each cell, group, or mobile station.

An embodiment of the present disclosure is useful to a mobilecommunication system.

REFERENCE SIGNS LIST

100 Transmitter

101 PT-RS generator

102, 203 Hopping pattern generator

103 Frequency hopper

104 Error correction coder

105 Modulator

106 Signal assigner

107 Transmitting unit

108, 201 Antenna

200 Receiver

202 Receiving unit

204 Signal demultiplexer

205 Channel estimator

206 CPE/ICI estimator

207 Data demodulator

208 Error correction decoder

The invention claimed is:
 1. A transmission apparatus comprising:circuitry, which, in operation, maps a phase tracking reference signalonto a subcarrier, which is determined by using an index foridentification of a mobile station and on which a demodulation referencesignal is mapped, a precoding applied to the demodulation referencesignal being the same as a precoding applied to the phase trackingreference signal; and a transmitter, which, in operation, transmits asignal containing the phase tracking reference signal.
 2. Thetransmission apparatus according to claim 1, wherein the phase trackingreference signal is mapped onto a subcarrier determined by using eitheran index for identification of a cell or group, or higher layersignaling.
 3. The transmission apparatus according to claim 1, whereinthe phase tracking reference signal is subjected to frequency hoppingevery unit time.
 4. The transmission apparatus according to claim 3,wherein the phase tracking reference signal is subjected to a hoppingoffset determined by using either an index for identification of a cell,group, or mobile station, or a time-domain index.
 5. The transmissionapparatus according to claim 4, wherein the time-domain index is asymbol number, a slot number, a minislot number, a subframe number, or aframe number.
 6. The transmission apparatus according to claim 4,wherein a plurality of the hopping offsets against a plurality of thephase tracking reference signals that are transmitted from a pluralityof antenna ports, respectively, are identical.
 7. The transmissionapparatus according to claim 1, wherein the circuitry, in operation,maps, at regular spacings in a frequency domain, a plurality of thephase tracking reference signals transmitted at a given time.
 8. Thetransmission apparatus according to claim 1, wherein the circuitry, inoperation, maps, at irregular spacings in a frequency domain, aplurality of the phase tracking reference signals transmitted at a giventime.
 9. The transmission apparatus according to claim 8, wherein thecircuitry, in operation, performs frequency hopping in a whole bandassigned to the mobile station and maps the plurality of the phasetracking reference signals onto any subcarriers within the whole band.10. The transmission apparatus according to claim 8, wherein the mobilestation is assigned a band divided into a plurality of partial bands,the circuitry, in operation, maps any one of the plurality of the phasetracking reference signals onto a corresponding one of the plurality ofpartial bands and performs frequency hopping on the phase trackingreference signal within the corresponding partial band.
 11. Thetransmission apparatus according to claim 1, wherein in a case wherethere is coordination among cells, the circuitry, in operation, maps, atregular spacings in a frequency domain, a plurality of the phasetracking reference signals that are transmitted at a given time and, ina case where there is no coordination among the cells, maps theplurality of the phase tracking reference signals at irregular spacingsin the frequency domain.
 12. The transmission apparatus according toclaim 1, wherein the phase tracking reference signal is mapped onto adifferent subcarrier for each cell, group, or mobile station.
 13. Atransmission method comprising: mapping a phase tracking referencesignal onto a subcarrier, which is determined by using an index foridentification of a mobile station and on which a demodulation referencesignal is mapped, a precoding applied to the demodulation referencesignal being the same as a precoding applied to the phase trackingreference signal; and transmitting a signal containing the phasetracking reference signal.